Epoxy-urethane polymeric compositions are known to possess physical properties which make them useful in applications such as elastomers, sealants and adhesives. Conventional epoxy resins such as those made by condensing epichlorohydrin with bisphenol A are readily and controllably cured by many types of materials to make products which exhibit high strength, but which are generally unsuitable for applications for which flexibility and elasticity are required.
By contrast, useful elastomeric materials can be made by the curing of urethane prepolymers (typically formed through the reaction of a diisocyanate and a glycol), using glycols, amino alcohols or diamines as vulcanizing agents. However, urethane-based resin compositions are known to present a number of practical problems, particularly in on-site mixed applications, stemming from the sensitivity of their cure chemistry to the presence of moisture and to the mix ratio. Typically, the use of urethane-based resin compositions as grouts, sealants or waterproofing membranes requires the on-site mixture of a resin component and a curative component in a specified mix ratio. Any departure from this mix ratio, which can readily occur by oversight or through the use of such two-component systems by unskilled persons, leads to unsatisfactory curing and inadequate physical properties of the cured resin.
A number of attempts have been made to produce resin-curative systems which exhibit at once the best features of both epoxies and urethanes. A curable liquid polyurethane-polyepoxide is described in U.S. Pat. No. 2,830,038 (Pattison). That material is prepared by reacting a polyurethane prepolymer with a hydroxy aliphatic epoxide compound such as glycidol. The resultant epoxide-terminated urethane prepolymer is then cured by mixing with polyamine compounds and heating for several hours at elevated temperatures.
U.S. Pat. No. 3,445,436 (Lake) similarly describes a sealant composition comprising a polyurethane prepolymer in which isocyanate groups are replaced by epoxy groups by reaction of a polyurethane prepolymer with hydroxy aliphatic epoxide compounds, or compounds containing an active hydrogen and aliphatic unsaturation capable of undergoing epoxidation in situ. Significant disadvantages presented by the preparation of the aforementioned known epoxy-urethanes stem from the high cost and relative instability of glycidol and of the related reactants employed to replace the isocyanate functionality of a urethane prepolymer with epoxide.
U.S. Pat. No. 4,143,009 (Dewey) describes a two-component composition for preparing an epoxy-urethane resin, in which the first component is a mixture of an organic diepoxide and a hydroxylakyl tertiary amine and the second part is an organic diisocyanate. The presence of free isocyanate groups in one of the resin components renders this composition subject to the disadvantages of urethane systems, principally susceptibility to moisture.
U.S. Pat. No. 4,262,288 (Burkhart) describes adhesive compositions formed by capping the polyester urethanes described in U.S. Pat. No. 3,763,079 (Fryd) with a dicarboxylic acid anhydride and chain-extending the capped polyester-urethane with an epoxy resin. The end products of this reaction are solids and must be dissolved in an appropriate organic solvent for use as adhesive compositions. Cross-linking (curing) of the dissolved epoxy-urethanes described by Burkhart is effected through available hydroxyl groups on the chain, using polyisocyanates or amino-formaldehyde resins, such as melamine-formaldehyde. It does not appear that curing of these epoxy-urethanes can usefully be effected through the epoxide functions of the chain, in contrast to the epoxy-urethanes of the present invention. The ability to use conventional epoxy curing agents is a substantial advantage of the epoxy-urethanes described and claimed herein, owing to the relative controllability and lower moisture sensitivity of the epoxy cure chemistry compared to that of isocyanates.
U.S. Pat. No. 4,520,185, issued to the same assignee as the present invention, relates to epoxy-urethane copolymeric materials which may be made by the reaction of epoxy resins with isopropyl and tertiary butyl alkanolamines to produce an epoxy-alkanolamine adduct, which is then reacted with urethane prepolymers. The product is a resin of block structure epoxy-urethane-epoxy which can be cured using conventional curatives effective in the curing of epoxy resins.